CCEJan/FebCHANNEL37,38 24/1/06 8:49 Page 37 PARTICLE BEAMS The future looks bright for particle channelling Techniques that make use of the ordered structure of a crystal lattice to manipulate particle beams are finding an increasing number of applications. Zn Cu (a) (b) (c) Fig.1. Radiographs using a parametric X-ray radiation beam: (a) foils of copper and zinc at 9 keV; (b) integrated circuit card and alumium step (?) at 13.5 keV; and (c) sample slice of a human tooth at 13.5 keV. (Courtesy Y Hayakawa et al.) When high-energy beams of charged and neutral particles interact that are useful in the multi-tera-electron-volt range. One new appli- with ordered matter, such as crystal lattices and nanostructures, cation proposes bending the LHC protons (or ions) by a huge angle they induce phenomena that are finding an increasing number of of 1–20° in the 0.45–7 TeV energy range using a bent single crys- applications at particle accelerators. This has led to a great deal of tal of silicon or germanium. This would allow calibration of the interest both in assessing the current state of the art of this fast- calorimeters in the CMS (or ATLAS) detector in situ, using an LHC growing field, and in stimulating research collaborations among the beam of precisely known energy. The simulations presented at the different groups involved. The International Workshop on Relativistic workshop show that such an application at the LHC is feasible. The Channelling and Coherent Phenomena in Strong Fields, held in workshop also reported results from the experiment at the Institute Frascati on 25–28 July 2005, provided an appropriate showcase for for High Energy Physics (IHEP), Protvino, on crystal bending of recent results in the field. The workshop was the latest in a series of 70 GeV protons by 9° (150 mrad) and its application for beam successful similar meetings and was merged with the Radiation delivery during 1994–2004. from Relativistic Electrons and Periodic Structures 2005 sympo- At lower particle-accelerator energies, crystal channelling can be sium in the biannual series that has been organized by Tomsk used to produce low-emittance beams useful for medical and bio- Polytechnic University since 1993. logical applications. The success in bending beams of less than 1 GeV was reported from the Beam Test Facility of the INFN’s Bent crystals Laboratori Nazionali di Frascati (LNF). Here, a positron beam of about Over the past decade, the understanding of particle steering by a 500 MeV provides the right energy scale for using the facility as a bent crystal lattice has progressed very well, and in particular the test bench for possible future applications of crystal techniques with accelerator applications of the bent-crystal channelling technique light ions in medical machines. This study was made possible through have greatly expanded (CERN Courier July/August 2004 p19). the support of Transnational Access to Research Infrastructure Crystal bending and extraction of particle beams has become an granted to LNF by the European Union as one of the major research established technology at high-energy accelerators, and with the infrastructures in Europe to give free access to researchers for the approaching start-up of the Large Hadron Collider (LHC) at CERN, period 2004–2008. The advances in crystal micro-technology for crystal-channelling techniques are providing further applications producing micro-beams for possible future applications in radio- ▲ CERN Courier January/February 2006 37 CCEJan/FebCHANNEL37,38 24/1/06 8:49 Page 38 PARTICLE BEAMS biology and medicine was also reported by the INFN-IHEP collabora- in radiography for biological samples such as teeth or bones (figure tion. This work covers the range from lower energies (kilo-electron- 1, p37). The contrast of the images was controlled with precise volts and mega-electron-volts) to higher energies (giga-electron-volts) changes of the X-ray energy, a great advantage of a system that and compares channelling techniques with alternative ones. uses a PXR beam. From Japan, a collaboration from Hiroshima University and KEK For the future, many interesting directions are foreseen in the reported on an experiment on electron-beam deflection with chan- field. A great deal of effort worldwide is being put into crystal radi- nelling in silicon crystals at the 150 MeV electron ring of the univer- ation research and applications. Further progress is expected in sity’s Relativistic Electron Facility for Education and Research. The applications using bent crystals for beam steering at accelerators. group plans tests with bent crystals at KEK’s Proton Synchrotron It will be an ideal opportunity to take full advantage of the chan- and aims to apply crystal deflection of high-energy beams at the nelling-crystal potentialities at the LHC and other high-energy accel- Japan Proton Accelerator Research Centre, the 50 GeV high-intensity erators, making crystals to serve for both collimation and extraction. proton machine currently under construction in Japan. The opportunity to have an extracted beam at a multi-tera-electron- volt machine should stimulate more research at the highest ener- Undulators and targets gies into particle interactions with aligned atomic lattices. The first While bent (and also focusing) crystals are well-known tools in accel- crystal-channelling undulators and their initial tests with positron erators, crystal undulators are just being introduced into experiments. beams should proceed to the realization of novel radiation sources; Channelling undulators offer sub-millimetre periods and magnetic thus, new positron-channelling experiments on undulator radiation fields of the order of 1000 T. Samples of crystal undulators have are eagerly awaited. already been manufactured and tested with X-rays and in channelling The success of the workshop is reflected both in the level of par- proton beams. Now tests using positron beams have been started at ticipation, with around 40 specialists coming from different geo- IHEP Protvino and at CERN’s Super Proton Synchrotron, and are also graphical areas, such as Europe, Japan and the former USSR, and planned at LNF. The first data from the experiment on positron radi- in the high quality of the presentations. The resulting papers will be ation in a crystal undulator at IHEP were presented at the workshop. published as a special issue of Nuclear Instruments and Methods The Yerevan Physical Institute presented calculations on radiation B, covering nearly all topics of current interest in channelling and produced by 20 MeV electrons channelled in the crystallographic radiation in aligned periodic structures at relativistic energies. planes of quartz, both with and without periodic deformations. The institute also plans experiments to study the influence of external Further reading fields on channelling radiation. For the proceedings of the previous workshop held in 2004 see: Intense positron sources using crystal effects are another applica- HHAndersen, S Bellucci, V M Biryukov (eds.) Nucl. Instrum. Meth. B tion of strong coherent fields. A number of talks reported on the the- 234 2005 1. ories of coherent radiation and pair production in ordered matter, and CERN’s WA103 collaboration reviewed the experimental progress Résumé in the field. The KEK–Tokyo–Tomsk–Paris collaboration reported a La canalisation des particules a le vent en poupe study of positron production from a thick silicon-crystal target using 8 GeV channelling electrons with high bunch charges. Les phénomènes induits par des faisceaux de particules de haute The workshop marked two decades since the experimental dis- énergie interagissant avec de la matière ordonnée trouvent covery of parametric X-ray radiation (PXR) in Tomsk in 1985: the toujours plus d’applications auprès des accélérateurs. Les radiation is generated by the motion of electrons inside a crystal, derniers résultats dans ce domaine en pleine évolution ont été such that the energy intensity of the radiation depends on the para- présentés à l'atelier international sur la canalisation relativiste et meters of the crystal structure. PXR has since been a subject of les phénomènes cohérents dans les champs intenses, tenu à experimental and theoretical research and possible applications at Frascati en juillet 2005. L’atelier a notamment porté sur la accelerators, and was a subject in many talks at the workshop. A canalisation dans les cristaux, tant à haute énergie, au LHC, qu’à team working at Nuclotron at the Joint Institute for Nuclear Research basse énergie, dans des applications médicales et biologiques, in Dubna has reported the first observation of PXR from moderately les onduleurs cristallins, les sources intenses de positons, et relativistic nuclei in crystals. A nice example of an application is a l’utilisation de rayonnement X paramétrique en radiographie. tunable monochromatic X-ray source based on PXR developed at the Laboratory for Electron Beam Research and Application in Nihon Stefano Bellucci, INFN/Frascati, and Valery M Biryukov, IHEP University, Japan. So far the main use of the X-rays there has been Protvino. 38 CERN Courier January/February 2006.